Device for protecting electric circuits from overheating



lllily' 27 1926. 1,593,760

0. DREYER nnvxcn FOR PROTECTING ELECTRIC cmcuns mom ovsmmume Filed April 25, 1924 2 sheetpshut 1 IIIIIII annual/"1",. I llllllllllll lllllllllll \llllllllllll Inwen or 2 0H0 Dreyer I Altai!) ey.

July 27 1926. 1,593,760

0. DREYER DEVICE FOR PROTECTING ELECTRIC CIRCUITS FROM OVERHEATING Filed April 25, 1924 2 s ti-shut 2 Invcn for:

0110 Dreyer by atented July 27, 1926.

UNITED STATES 1,593,760 PATENT OFFICE.

OTTO DBEYER, OF ESSEN-ON-THE-BUHR, GERMANY.

DEVI ZOE FOR PROTECTING ELECTRIC CIRCUITS FROM OVERHEATING.

Application filed April 25, 1924, Serial No. 708,995, and in Germany February 29, 1824.

The invention relates to devices for protecting' electrical circuits from over-heating of the type whereby the circuit which is in danger is disconnected by means of an interchangeable releaser, which consists essentially of a sleeve or casing having a pin switch or contact rod which is soldered therein with easily fusible material, and, when the solder softens, is pressed forwards by means of a spring and thereby initiates the process of disconnection.

In the known devices of this type the releaser must in general be replaced by a new releaser after each time it has come into operation, i. e. it must be exchanged. According to the present invention, the necessity for this exchange is avoided, by making the releaser of similar form at both ends, and in such a manner that, after once having come into operation, it can beused again by simply reversing it. To this end the casing of the releaser is provided at both ends wit openings for the passage of the correspondingly long contact rod, and the spring which acts on the latter is arranged externally of the casing, in such a manner that it is strained when the releaser is inserted and tends to press the contact rod into the opposite end position. It is recommended that the casing which contains the contact rod should be formed as a piece of tube open at both ends, which is either itself capable of being inserted in and held by the heating coil which surrounds it or is combined with the latter to form-a cartridge which can be inserted as a unit and can be fitted in a small porcelain case having a screw cap of the same or similar construction as for the known safety cartridge fuses.

The opposing contact with which the contact rod co-acts can be arranged either at the bottom of this casing or on its screw-cap or near the latter. When, in particular, only a limited space is available, as, for example when arranged in a closed fusebox, it is recommended that the opposing contact should be arranged on the inside of the cover of the box, in which case the conb t h member actuated y it, mus pass t rou an o enin rovided in the screw c ver of the gaslng. Such a compact form of construction can be obtained in this manner that the com lete protecting device can be built in the orm.

of usual safety elements and fitted eside or between these in the ordinary fuse boxes.

Various constructional embodiments of the invention are illustrated by way of example in the accompanying drawing in which, t

Fig. 1 shows in longitudinal section a temperature-protecting-element for currents of small stren Figs. 2 and 3,. a modified form of construction of the head of the plug of the protecting element of Fig. 1, v

Figs. 4 and 5 show respectively the arrangement of the protecting element according to Fig. 1 in combination with two normal safety elements in one fuse box, in section and in plan, the cover of the box lfi eing swung open and partly shown in Fig. 6, a diagram of connections for the protecting device according to Figs. 1-3,

Fig. 7, a form of protecting element for currents of greater strength, and

Fig. 8 the special form of plug-in releaser for protecting elements according to Fig. 7.

Referring now to the embodiment illustrated by way of example in Fig. 1 of'the drawings, 1 is the socket which is made of porcelain or other suitable insulating material, and 2 is the heating coil which is traversed by the current in the circuit which is to be protected. The coil 2 possesses essentially the external form of a safety cartridge fuse and is held fast in the casing, so that it is easily interchangeable and electrically connected, in the same manner as the latterby means of the plug-head 4 which contains, as usual, 9. sheet-metal cap 3 having an Edison-thread. The current supply takes place by means of the terminal 5 through the screw-socket 6 and the screw means of an easily fusible metal while its enlarged ends 10 and 10" are guided in the wider art of the sleeve 7 and, in the posi-" tion 0 rest illustrated, the lower of the two" ends, namely,10" projects out of the sleeve. From the sleeve 7 the current flows through the lower flange 8 and a foot-ring 11 WhlCll is held in the socket 1, to the terminal 12. In the ring 11 and guided by it there is fitted a plate 15 which is movable therein and is acted upon by the spring 14 which tends to press t e releasinfg pin upwards but is ordinarily prevented rom doing so by the soft-soldered joint. The upper end 10 of the releaser projects into an opemng 16 provided in the plug-head 4 where at a certain distance from the end 10 is also situated the opposing contact 17 which is arranged, for example, on the cover of the pertaining fuse-box, and which, as may be seen from the corresponding diagram of connections, Fig. 6, is connected also with the second pole of the current leads.

If now, owing to inadmissible heating up of the current consumer or of the heating coil, the soldered joint softens, the releasing-pin 10 is pressed upward by the action of the spring 14 until, on touching the opposing contact 17, it short-circuits the supply leads to the current consumer and thereby causes the fuses 18, 19 to blow, that is to say it cuts off the circuit which is in danger. When the circuit has been disconnected the entire heating coil can easily be taken out after the plug-head 4 has been unscrewed, and, assuming that the soldered joint has meanwhile cooled down sufliciently and become fast, can be replaced by inserting it again in the element in an inverted position, that is with the end of the contact rod which has protruded from the top towards the bottom, and fixed by screwing on the plug head, whereby the spri 14 is simultaneously again com ressed. 3%9 device is then, after any ses which may have blown have been replaced, ready for use without further trouble.

In order to avoid making contact with the upwardly projecting live end of the releaserwhen screwing the plug-head on again, it is advantageous not to allow the releasing-pin itself to pass through the plug head, but as is shown n Figs. 2 and 3, to arrange an intermediate contact member 20, which is fitted 'movabl in the plug head 4 and is normally held y the action of the spring 21 in the position illustrated in Fig. 2, that is, it is held in the drawn-in position, at the same time it is of such short dimensions that it does not touch the upper end of the releasing-pin, and'therefore is not alive, so that the plug-head can be screwed tight without danger. If, however, the releasingpin advances on the softening of the soldered joint, it first makes contact with the intermediate member and presses it forward against the action of the spring 21, as shown in Fig. 3, until the latter makes contact with the opposing contact 17 which is fitted on the cover of the safety element, whereby the endangered circuit is disconnected.

With the compact construction of heating coil and re-usable releaser illustrated in Figs. 1-3, :the whole device, as may be seen from Figs. 4 and 5, may be easily and advantageously employed together with the usual elements for the two circuit protectors 18, 19 and may be suitably fitted between them in a common fuse-box 25-,- on the cover 26 of which the opposing contact 17 is fitted. The latter is connected by means of a spring metal strip 27 with the contact 28 of the other pole, which is fixed in the lower part of the box, and against which its sprin as shown in Fig. 4, when the box is c osed thereby conductingvthe electric potential to the contact 17. If however, the cover 26 be raised the contact at 27, 28 is broken and the metal parts fastened to the cover become dead, so that it is possible to put the protecting device into order a ain without danger. Whether the device as operated and must be re-set, can easily be ascertained on raising the cover, by the intermediate con necting member 20 projecting out of the plug-head 4, while the condition of the two adjacent fuses can be acertained in the usual manner by means of the indicating plate of the cartridge fuse which is visible through the sight hole of the plug.

Again, the contact upon which the temperature releaser acts, particularly in the case of safety elements for currents of greater strength, instead of being arranged outside the element, can in some cases be arranged in its foot, as is illustrated by way of exam le in Fig. 7, when, on the softening of t e soldered joint, the contact between the two parts 31, 32 is broken by the sprin 30. The construction illustrated in Fig. 7 1s however also different from that of the first example in so far as the sleeve 7 of the temperature releaser is not fixed in the heating coil but is held loosely, so that it is capable of being pushed in, in a bush 34 which is fixed in the coil. In this case the spring tends to hold the releaser 7, 10 in the pushed-in position, which is limited in the upward direction by the projecting part 35 of the bush 34. Thus, it is no longer the complete heating coil together with the releaser which is insertable but the latter is itself arranged so that it is capable of being inserted in the heating coil, which can be removed for this purpose after the plug head has been unscrewed.

This arran ment possesses also the special advantage t at the actual insertable temperature releaser is extraordinarily simple, as may be seen from Fig. 8, and can easily be exchanged if necessary for another similar releaser, having its soldered joint made with more easily or more difliculty fusible metal,

according as it is desired that the circuit to be protected should be disconnected earlier or later. By this means one and the samelating case, comprising a body and a cover detachably connected therewith, said cover having an opening, an axially perforated heat coil in said case in cartrid e form, said coil being disposed mutually within the casing and its cover and removably held between the same, a guide tube within the axial perforation of said cartrid e, a releaser pin, adapted for longitu inal reciprocation within said guide tube, in line with the opening in the cover but normally securable therein in an end position by a thin layer of heat responsive material of predetermined meltin point, in which position one end of the in is retracted relative to the opening in t e cover, means urging said releaser pin from the one end position into the other relative end position, whereby upon the release of the pin the pin will be moved to project its first named end relative to said opening in the cover, said guide tubetogether with said releaser pin being readily reversible, end for end in said casing and binlding posts connected to the ends of the e01 2. In a safety device of the character set forth, in combination with a base 1' two stationary contact members, a t

contact member independent of-said base a releaser cartridge,- com risin an axially perforated heatin e01 umt removably mountable on said ase in electric series'contact with said two stationary contact members, a sleeve mounted in said axial coil perforation, a double-ended releaser pin 0 rable within said sleeve, a heat contro led solder joint between said sleeve and said pin adapted to normally retain said pin in its inoperative end position, and means-urging said pin into its operative endlpositionin contact with said third contact member upon said solder joint being broken by excess heat in said coil.

.3. In a safety device according to claim 2,- ,an intermediate member in axial alinement with, and operable by, said releaser in, interposed in normally spaced relation tween said releaser pin and said third contact member, and means, weaker than said pin-urging means, normally retaining said intermediate member out of contact with said third contact member.

4. In a safety device of the character set forth, in combination with a base carrying two stationary contact members for the one circuit mai-n, a third contact member for the other circuit main, a releaser cartrid e, comprising an axially perforated heatlng coil unit removably mountable on said base by screw-theaded engagement in electrical seriescontact with said two stationary contact members, and a cover for saidcoil unit presenting a top depression merging into a central coil er oration, said third contact member over anging said top depression, a metal sleeve in said axial coil perforation, a releaser pin presenting identical contact extremities operable within said sleeve, a fusible joint between said sleeve and said pin, said 'oint being broken upon the heat of said eating coil exceeding a predeterminable degree, and said pin normall relatively retained in its inoperative en position by said fusible joint, and means tending to force said pin through said central cover perforation into contact with said third contact member upon said fusible joint being broken.

5. In a safety device according to claim rforation in alinementwith said 4, a case housing said base and cartridge, a

cover for said case, and said third contact member being so mounted within said case that it is automatically cut out of the circuit on opening of said cover and cut inon -and adapted to having its leads short circuited by the pin engaging the contact, and fusible means holding the pin inoperative, said contact being removed from the path of the pin upon opening the cover.

In testimony whereof I afiix my signature.

o'r'ro DREYER. 

